This invention relates to an electret microphone which has an impedance conversion element disposed in a capsule.
In conventional electret microphones of this kind, an impedance conversion element such as, for example, a field effect transistor is built in a capsule for the impedance conversion of an electric output signal. With such an arrangement, when soldering a terminal of the impedance conversion element to a printed circuit board, heat generated by the soldering causes a change in the air pressure in a compartment defined on the back of a back electrode which warps the electret diaphragm formed of a synthetic resinous material, providing degraded sensitivity; moreover, a hole is made in the soldered portion to intercommunicate the compartment and the outside, resulting in deteriorated frequency characteristic.
It is an object of this invention to provide an electret microphone whose sensitivity is not affected by soldering of an impedance conversion element.
It is another object of this invention to provide an electret microphone whose frequency characteristic is not degraded by soldering of an impedance conversion element.
It is another object of this invention to provide an electret microphone which exhibits sensitivity from low to high frequency region and hence has a wide frequency band.
It is still another object of this invention to provide an electret microphone which is mechanically stable in its internal structure.